Linear unit for transferring objects

ABSTRACT

A linear unit for transferring objects, particularly for removing workpieces from a linear conveying track, comprising vertically and horizontally movable grippers for grasping the objects and comprising a gripper carriage which is movable between a pick-up position and delivery position and having first and second carriage parts, wherein the movement sequence of the grippers for receiving the objects in the pick-up position and for depositing the objects in the delivery position is effected due to relative movement of the second carriage part with respect to the first carriage part.

BACKGROUND OF THE INVENTION

The invention relates to a linear unit for transferring objects,particularly for removing workpieces from a linear conveying track, suchas an assembly or manufacturing belt, and comprising vertically andhorizontally movable grippers for gripping an object and supported on agripper carrier movable between pick-up and delivery positions.

For example, in assembly or production lines, such linear units serve tograsp and transfer workpieces which are transported on a linearconveying track, e.g. conveyor belt, e.g. to a second conveyor belt orto a processing station. For this purpose, the grippers are moved by agripper carrier to a pick-up position, where they grip the workpiece,and then to a delivery position, where they deposit the workpiece again.Costly control mechanisms are required for the coordinated interplay ofthe gripper movements necessary for gripping and depositing.

SUMMARY OF THE INVENTION

The object of the invention is to simplify the structure of the linearunit for transferring objects.

This object and others which will become more apparent hereinafter isattained by providing a linear movement in which the movement sequenceof the grippers for picking up an object at the pick-up position anddepositing it at the delivery position is caused by an excess lift ofthe gripper carrier after it reaches the pick-up and delivery positions.The sequence of movements for gripping or depositing the objects ispositively controlled mechanically and is carried out automatically bythe excess lift of the gripper carrier after it reaches the pick-up anddelivery positions, respectively.

It has proven advisable to divide the sequence of movements of thegrippers into a horizontal rotational or swiveling movement and avertical displacing movement which are carried out one after the otherand in the reverse sequence in the pick-up and delivery positions. Thesetwo portions of the movement sequence can be achieved by means of theexcess lift of the gripper carrier in a simple manner by providing atoothed rack and pinion gearing between the gripper carrier and gripperand by forming the grippers of vertical gripping arms and horizontalgripping fingers which are coupled with one another via a coarse threadconnection in each instance. This has the advantage that the individualphases of the movement sequence need not be adapted to the size of therespective object to be transferred, but are independent of this.However, the workpieces are held with the same gripping force regardlessof their size. The gripping technology used in the linear unit,according to the invention, is accordingly independent of the size ofthe object, wherein the maximum size of the workpieces to be grasped is,of course, determined by the distances of the vertical gripping armsfrom one another.

It is possible to feed and guide away the object to be transferred orgripped on all sides of the linear unit when four vertical gripping armsare provided so as to be equidistant from one another.

An additionally increased gripping force which ensures a secure holdingof the gripped object during the movement of the gripper carrier isimparted to the gripping fingers at the end of the movement sequence byforming the coarse thread connection having a length that is less thanthe excess lift of the gripper carrier with the gripping fingerscontacting the object in a force-locking manner. The lifting movement ofthe gripping fingers is defined by the end of the coarse-threadconnection and the remaining slight residual excess lift of the grippercarrier forces a rotation of the gripping arms and, accordingly, anincreased contact pressure of the gripping fingers at the object whichis already gripped and lifted.

The excess lift of the gripper carrier required in the end stations ofthe gripper carrier, that is, in the pick-up and delivery position, whenthe grippers are positioned can be achieved in a simple manner byconstructing the gripper carrier as a carriage which reciprocatesaxially and comprises two carriage parts displaceable relative to oneanother. One carriage part is being driven to provide reciprocatingmovement of the carriage, and the second carriage part carries grippersin a fixed spaced relationship relative to one another. The excess liftresults from relative movement of the carriage parts which is caused bystops at the ends of the carriage movement.

Other advantageous developments and improvements of the linear unit willbecome apparent from the following detailed description of the preferredembodiment with reference to appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a conveying device with two conveyor beltsand a linear unit according to the invention for transferring workpiecesfrom one conveyor belt to the other;

FIG. 2 shows a cross-sectional view of the linear unit along to lineII--II in FIG. 1;

FIG. 3 shows an exploded view of a gripper of the linear unit shown inFIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The conveying device for workpieces designated by 10, which can be seenin a side view in FIG. 1, comprises two linear conveying tracks in theform of two double-belt conveyor belts 11, 12 which extend horizontallyrelative to one another. In order to transfer the workpieces 10 from oneconveyor belt 11 to the other conveyor belt 12, a linear unit 13 isprovided which comprises a gripper arrangement comprising four grippers14 constructed in pairs in a mirror-inverted manner and a longitudinallydisplaceable gripper carrier 15 which can be moved between a pick-upposition 16 and a delivery position 17.

The gripper carrier 15 is constructed as a longitudinally displaceablecarriage 18 which comprises an upper carriage 19 and a lower carriage 20having the same longitudinal dimensions. The upper carriage 19 is guidedon two sliding bars 21 so as to be longitudinally displaceable and isdriven to provide for displacing movement of the carriage. Thedisplacing movement is defined by two end stops 22 and 23 which extendalong the vertical front dimension of the upper carriage 19 as well asalong the vertical front dimension of the lower carriage 20. The lowercarriage 20 carries a spacing piece 24 on its front side facing the endstop 22. The upper carriage 19 and lower carriage 20 are displaceablerelative to one another, wherein the maximum displacing path h_(rel) ofthe two carriages 19, 20 relative to one another and the excess lifth_(rel) of the upper carriage 19 relative to the lower carriage 20 isdetermined by the length of the spacing piece 24. The movement sequenceof the grippers 14 for picking up a workpiece 10 in the pick-up position16 and for depositing the workpiece 10 in the delivery position 17 isforced after reaching the pick-up and delivery positions 16, 17,respectively, by means of this excess lift h_(rel).

Every gripper 14 comprises a vertical gripping arm 25, which issupported so as to be rotatable in the lower carriage 20 with a collar36, and a gripping finger 26 which is movable in a swiveling manner onthe gripping arm 25. As can be seen clearly in FIG. 3, the gripping arm25 carries a toothed pinion 27 at one of its ends so as to form onepiece and is provided at the other end with a helix 28 having a definedaxial length 1. The toothed pinion 27 meshes with a toothed rack 29which is fastened to the upper carriage 19. The upper carriage 19accordingly carries a total of four toothed racks 29 which are arrangedon a side of the assigned toothed pinion 27 such that during therelative displacement of the upper carriage 19 in one displacingdirection, a resulting rotational movement of the gripping arm 25,causes swivelling of the gripping fingers 26 toward one another in aclosing movement for the workpiece 10, and during the displacement ofthe upper carriage 19 relative to the lower carriage 20 in the oppositedirection the inverse rotating direction of the gripping arms 25, whichis brought about by means of this, swivels the gripping fingers 26 awayfrom one another in an opening movement for the workpiece 10. Thegripping finger 26 which projects away from the gripping arm 25 at aright angle comprises a bushing 30 which is coaxial with the grippingarm 25 and overlaps the helix 28. The helix 28 is constructed so as tohave three threads, and the inner wall of the hollow-cylindrical bushing30, in a corresponding manner, carries three sliding cams 31 which areoffset relative to one another at the circumference, one sliding cam 31engaging in each instance in a helix thread of the helix 28. Thegripping finger 26 carries a gripping surface 32 at the front end withwhich the gripping finger 26 contacts the workpiece 10 to be grasped. Astop disk 33 is fastened, e.g. with a countersunk screw 34, on the frontside of the gripping arm 25 defining the helix 28. A helical pressurespring 35 is placed on the gripping arm 25 and is supported on one sideat the bushing 30 of the gripping finger 26 and on the other side at thelower carriage 20, so that the gripping finger 26 is constantly loadedin the direction of the stop disk 33. Each gripping finger 26 on eachgripping arm 25 contacts the stop disk 33 when the gripper arrangementis opened, that is, when the workpiece 10 is not gripped (FIGS. 1 and2).

The movement sequence of the grippers -4 which is forced by the excesslift h_(rel) of the upper carriage 19 relative to the lower carriage 20in the pick-up position 16 and in the delivery position 17 of thecarriage 18 is divided into a horizontal swiveling movement and avertical displacing movement of all the gripping fingers 26 due to thetoothed rack and pinion gearing 27, 29 between the upper carriage 19 andthe gripping arm 25 and as a result of the helix-and-sliding camconnection 28, 31 between the gripping arm 25 and the gripping finger26. In the pick-up position 16, the horizontal swiveling movement isfollowed by the vertical displacing movement, whereas in the deliveryposition 17 the gripping fingers 26 first execute a vertical displacingmovement and then a horizontal swiveling movement. In the pick-upposition 16, in which the workpiece 10 is gripped, the horizontalswiveling movement of the gripping fingers 26 is a closing movementdirected toward the workpiece 10 and the vertical displacing movement isa lifting movement lifting the workpiece 10; whereas, in the deliveryposition 17, the vertical displacing movement of the gripping fingers 26is a lowering movement and the horizontal swiveling movement is anopening movement directed away from the workpiece 10. The axial length 1of the helix 28 is dimensioned somewhat smaller than the excess lifth_(rel) of the upper carriage 19 relative to the lower carriage 20. Thelifting movement of the gripping fingers 26 is accordingly terminatedsomewhat sooner than the rotation of the gripping arms 25 caused by thetoothed rack portions 29 and the toothed pinion 27. Accordingly, in thisremaining residual lift, the gripping fingers 26 fixed on the grippingarms 25 after the end of the lifting movement are turned slightlyfurther in the direction of the workpiece 10. However, since thegripping surfaces 32 of all the gripping fingers 26 already contact theworkpiece 10 in a force-locking manner, the contact pressure force ofthe gripping fingers 26 at the workpiece 10 is increased by means ofthis rotating movement of the gripping arms 25, so that a reliableholding of the workpiece 10 in the gripper arrangement formed from thefour grippers 14 is ensured during the movement of the carriage 18.

The linear unit operates as follows during the transferring of aworkpiece 10. The workpiece 10 is brought into the pick-up position 16of the linear unit 13 with the double-belt conveyor belt 11. Thecarriage 18 is displaced toward the left, as seen in FIG. 1, toward theend stop 22. The lower carriage 20 impacts at the end stop 22 with itsspacing piece 24 and its movement is blocked. The upper carriage 19continues to move until it likewise contacts the end stop 22, wherein itcovers the distance of the excess lift h_(rel). All gripping arms 25 arerotated by this excess lift h_(rel) via the toothed racks 29 and thetoothed pinions 27 (the gripping arm 25 shown in FIG. 3 executes arotation in the counterclockwise direction). All gripping fingers 26 areswiveled toward the workpiece 10 by these rotating movements of thegripping arms 25 until their gripping surfaces 32 contact the workpiece10. The horizontal swiveling movement of the gripping fingers 26 isaccordingly blocked, and the continued rotating movement of the grippingarms 25 leads to a lifting movement of the gripping fingers 26 via thehelix 28 and the sliding cams 31 sliding in the latter, so that theworkpiece held by the gripping surfaces 32 is lifted vertically from theconveyor belt 11. An additional closing movement of the gripping fingers26 in the direction of the workpiece 10 is effected at the end of thehelix 28--as was described above--by means of a slight residual rotationof the gripping arms 25, so that the holding force with which theworkpiece 10 is held by the gripper arrangement is increased. FIG. 2shows the gripping finger 26 of the right-hand gripping arm 25 duringits closing movement toward the workpiece 10, while the gripping finger26 of the left-hand gripping arm 25 is shown after the end of itslifting movement The helical pressure spring 35 is compressed during thelifting movement of the gripping finger 26.

The carriage 18 is now moved into the right-hand delivery position 17,as seen in FIG. 1, by the drive of the upper carriage 19. In thedelivery position 17, the lower carriage 20, which projects over thefront side of the upper carriage 19 by an amount corresponding to theexcess lift h_(rel), impacts at the end stop 23 with its front side andits displacing movement is blocked, while the upper carriage 19 canstill move until the end stop 23 by an amount corresponding to theexcess lift h_(rel). All gripping arms 25 are rotated again by thisrelative movement of the upper carriage 19 relative to the stationarylower carriage 20. The excessive gripping force is first reduced, then alowering movement of the gripping fingers 26 is carried out until thegripping fingers 26 contact the stop disks 33 at the end of the grippingarms 25 accompanied by the action of the helical pressure springs 35.The gripping fingers 26 are accordingly rigidly connected with thegripping arms 25 and the additional rotating movement of the grippingarms 25 causes a horizontal swiveling of the gripping fingers 26,wherein the gripping surfaces 32 move away from the workpiece 10. At theend of the rotating movement of the gripping arms 25, the grippingfingers 26 occupy the position seen in FIG. 1. The workpiece 10 isdeposited on the conveyor belt 12 and is transported away by the latterfrom the delivery position 17. The described process is repeated everytime a workpiece 10 is transferred.

The invention is not limited to the described embodiment example. Thus,the spacing piece 24 for determining the excess lift of the uppercarriage 19 can also be arranged at the end stop 22. The helix 28 on thegripping arm 25 and the sliding cams 31 on the inner wall of the bushing30 which slide in the helix 28 can also change places.

In a preferred embodiment, end stops 22, 23, 24 are assigned only to thelower carriage 20 carrying the grippers 14, and the lower carriage 20 issupported between axial stop shoulders of the driven upper carriage 19so as to be displaceable at the upper carriage 19 by a distancecorresponding to the excess lift h_(rel). This has the advantage thatthe excess lift h_(rel) is a fixed magnitude independent of theadjustment of the pick-up and delivery positions of the lower carriage20 and the grasped workpieces and workpiece carrier, respectively, areheld with the same contact pressure force of the gripping fingers 26.

If the force-locking engagement between the gripping fingers 26 and theworkpiece or workpiece carrier brought about solely by the helicalpressure spring 35 in connection with the helix drive 28, 31 issufficiently great, the length of the helix 28 can be dimensioned insuch a way that there is still free helix length available at the end ofthe relative movement between the two carriage parts 18, 20. In thiscase, workpieces and workpiece carriers whose dimensions deviate fromone another within certain limits can also be grasped and transferred.Of course, the required rotating movement of the gripping arms until thestop of the gripping fingers at the object will be smaller with a largeworkpiece than with small objects. However, the residual rotation of thegripping arms forced by the toothed rack and pinion gearing is convertedinto a lifting movement of the gripping fingers, so that largerworkpieces can be lifted correspondingly farther than smallerworkpieces.

The described embodiment can only receive a workpiece in one endposition of the carriage 19, 20 and deposit in the other end position.However, the arrangement can also be carried out in an advantageousmanner in such a way that a pick-up and depositing is possible in bothend positions, i.e. in such a way that transportation can be effected inboth directions. For this purpose, means are provided, e.g. a secondpneumatic drive, which displace the lower carriage 20 relative to theunmoved upper carriage 19 by an amount corresponding to the excess lifth_(rel) in every end position

We claim:
 1. A linear unit for transferring workpieces located on anassembly or manufacturing belt, said linear unit comprising a firstcarriage part horizontally displaceable along support structures betweenpick-up and delivery positions; a second carriage part displaceableparallel to said first carriage part and connected for movementtherewith by friction contact; a gripper supported on said secondcarriage part for rotation about a vertical axis for grasping aworkpiece; stop means ending in a displacement path of said secondcarriage part, said stop means shortening the displacement path of saidsecond carriage part relative to a displacement path of said firstcarriage part and providing for movement of said second carriage partrelative to said first carriage part when said first carriage partreaches one of the pick-up and delivery positions; and drive means forconverting the relative movement of said first and second carriage partsinto horizontal rotational and vertical movement of said gripper, saidgripper including a vertical gripper arm and a gripper finger rotatablysupported on said gripper arm, said drive means including a pinionfixedly supported on said gripper arm, a toothed rack associated withsaid first carriage part and engaging said pinion for providing ahorizontal rotational movement that corresponds to one of closing andopening movements of said gripper, and coarse thread connection meansarranged between said gripper arm and said gripper finger and engagablewith said gripper finger for providing a vertical movement thatcorresponds to one of pick-up and delivery movements of said gripper. 2.A linear unit as set forth in claim 1 wherein said gripper arm has afree end, said linear unit further comprising a stop disc arranged atsaid free end of said gripper arm; and a return spring for biasing saidgripper finger into engagement with said stop disc, said coarse threadconnection means including a coarse thread having a pitch which is soselected that a torque applied to said gripper by said return spring incooperation with said coarse thread causes a rigid connection of saidgripper finger with said gripper arm upon relative rotational openingmovement at which said gripper finger moves away from engagement withthe workpiece.
 3. A linear unit as set forth in claim 2 wherein saidreturn spring is formed as a helical compression spring mounted on saidgripper arm and having opposite ends engaging said gripper finger andsaid second carriage part, respectively.
 4. A linear unit as set forthin claim 1 wherein said coarse thread connection means includes amultiple thread helix arranged on one of said gripping arm and saidgripping finger and a plurality of cams arranged on the other of saidgripping arm and said gripping finger, corresponding in number to anumber of threads of said helix, and guided in said helix.
 5. A linearunit as set forth in claim 1 wherein said coarse thread connection meanshas an axial length which is less than a magnitude of relative movementbetween said first and second carriage parts.
 6. A linear unit as setforth in claim 1 wherein said stop means includes a plurality of stopsdefining said pick-up and delivery positions and extending along endpositions of both of said first and second carriage parts, said firstand second carriage parts having an identical end position in adirection of joint movement thereof, said linear unit further comprisinga spacing member extending in the direction of joint movement of saidfirst and second carriage part and arranged on one of an end surface ofsaid second carriage part and a stop facing said end surface, saidspacing member having a length that defines a magnitude of relativemovement between said first and second carriage part.